1. Field of the Invention
This invention relates generally to slide fasteners and particularly to coupling elements mounted thereon which are taken into and out of engagement with each other to close and open the slide fastener. More particularly, the invention is concerned with such coupling elements made of a metallic material and arranged in an individual discrete formation.
2. Prior Art
Individual coupling elements for slide fasteners are usually press-formed from a metal blank into the desired shape and planted in a row on and along a beaded longitudinal edge of a support fabric tape. Among conventional metallic materials for slide fastener coupling elements are known aluminum alloys, copper alloys such as nickel silver, red brass, brass and the like. The coupling elements are surface-treated by various known processes to provide thereon a protective layer of film for purposes of resistance to abrasion and corrosion, or a colored film layer for purposes of ornamental or aesthetic appeal.
There have been proposed various processes and techniques for providing such protective or ornamental films on metal surfaces which include coating, anodic oxidation such as disclosed in Japanese Patent Publication 58-25760 and chemical film formation such as disclosed in Japanese Laid-Open Patent Publication 57-93003.
The above known processes however have their inherent problems. The resulting coated films were susceptible to wear and separation from the surfaces of the fastener elements during repeated manipulation of the slider or laundering of the fastener articles. Anodic oxidation processes, being electro-chemical, involved highly costly equipment and facilities leading to increased cost of the product fastener elements. Chemical film forming processes were also objectionable in that waste fluids produced from this process would pose environmental pollution problems and the resulting film per se is weak and fragile.